1. Field of the Invention
The present invention relates to an exposure chuck and a method for fabricating a liquid crystal display (LCD) device using the same, and more particularly, to an exposure chuck capable of preventing the generation of stains in an exposing process while fabricating an in-plane switching mode LCD.
2. Discussion of the Related Art
Flat panel display devices having useful advantages, such as providing a high quality picture and operation at low power consumption rate, are becoming commercially used display devices. One type of the flat panel display devices includes liquid crystal display (LCD) devices generally including a thin film transistor (TFT) array substrate and a color filter substrate facing each other. The two substrates are positioned at some distance from each other and a liquid crystal layer is formed in the interval of the two substrates.
On the TFT array substrate, pixels are arranged in a matrix configuration identifying unit pixels, and a TFT, a pixel electrode, and a capacitor are formed in each of the unit pixels. On the color filter substrate, a common electrode for applying an electric field to the liquid crystal layer, an RGB color filter for implementing actual colors, and a black matrix are formed. An alignment layer is formed on the surface of the TFT facing the color filter substrate and a rubbing operation is performed, thereby arranging the liquid crystal layer in a same direction as the rubbing direction. When the electric field is applied between the pixel electrode formed in each of the unit pixels on the TFT array substrate and the common electrode formed at the front surface of the color filter substrate, the liquid crystal layer passes light or shields light by a dielectric anisotropy that rotates molecules of the liquid crystal layer, to display characters or images. However, the twisted nematic mode LCD device has a disadvantage such that a viewing angle is narrow. Accordingly, an in-plane switching mode LCD is actively researched to increase the viewing angle by arranging the liquid crystal molecules to be parallel with a substrate.
FIGS. 1A and 1B illustrate a unit pixel of an in-plane switching LCD according to the related art. FIG. 1A is a plane view of the in-plane switching LCD, and FIG. 1B is a cross sectional view along I-I′ of FIG. 1A. As shown, a gate line 1 and a data line 3 are horizontally and vertically arranged on a transparent first substrate 10 to define a pixel region. For the convenience of discussion, only one pixel is illustrated in FIGS. 1A and 1B. The in-plane switching LCD device may include n number of gate lines and m number of data lines, thereby defining an n x m matrix of pixels. At an intersection of the gate line 1 and data line 3, a thin film transistor 9 composed of a gate electrode la, a semiconductor layer 5, and source/drain electrodes 2a and 2b is formed. The gate electrode la and the source/drain electrodes 2a and 2b are respectively connected to the gate line 1 and the data line 3. In addition, a gate insulating layer 8 is formed on the entire substrate 10.
In the pixel region, a common line 4 is arranged in parallel with the gate line 1, and a pair of electrodes, a common electrode 6 and a pixel electrode 7, are arranged in parallel with the data line 3. The common electrode 6 and the pixel electrode 7 switch an orientation direction of liquid crystal molecules of the liquid crystal layer 13 when horizontal electric field is formed between the common and pixel electrodes. The common electrode 6 is simultaneously formed with the gate line 1 and is connected to the common line 4, and the pixel electrode 7 is simultaneously formed with the source/drain electrodes 2a and 2b and is connected to the drain electrode 2b of the thin film transistor 9. A passivation layer 11 is formed on the entire substrate 10 including the source/drain electrodes 2a and 2b. A pixel electrode line 14, which overlaps the common line 4 and is connected to the pixel electrode 7, forms a storage capacitor Cst such that the insulating layer 8 is positioned between the common line 4 and the pixel electrode line 14.
On a second substrate 20, a black matrix 21 is formed to prevent light from leaking to the TFT 9, the gate line 1, and the data line 3, and a color filter 23. In addition, an overcoat layer 25 for planarizing the color filter 23 is formed on the color filter 23. Alignment layers 12a and 12b for determining an initial alignment direction of liquid crystal molecules are formed on the surfaces of the first substrate 10 and the second substrate 20, respectively. A liquid crystal layer 13 is formed between the first substrate 10 and the second substrate 20, thereby controlling transmittance of light by voltages applied to the common electrode 6 and the pixel electrode 7. In the in-plane switching LCD device, the common electrode 6 and the pixel electrode 7 are arranged on the same substrate and generate a horizontal electric field, thereby increasing a viewing angle of the LCD devices. However, since the common electrode 6 and the pixel electrode 7 are made of an opaque metal arranged in the pixel region which lower an aperture ratio, brightness of the LCD devices is degraded. Accordingly, a research to increase the aperture ratio is actively conducted by forming either the common electrode 6 or the pixel electrode 7 from indium tin oxide (ITO) or indium zinc oxide (IZO).
The in-plane switching LCD device of FIGS. 1A and 1B is fabricated by multiple photo-lithography processes including a process for depositing a photoresist, an exposing process, a development process, and an etching process. The exposing process is performed on the substrate using a mask to selectively shield a portion of substrate from light irradiated by an exposing device. First, a layer is formed on the substrate where a pattern is formed. Next, a photoresist is deposited on the layer, and the substrate is loaded onto the exposing device, wherein the substrate and the mask are aligned and light is irradiated on the photoresist through an opening of the mask. At this time, the substrate is placed on a chuck and fixed so that any misalignment between the substrate and the mask may be prevented. During the exposing process, an electrostatic filed is generated due to friction between the substrate and the chuck, wherein foreign materials may be attached onto the substrate. In order to minimize the foreign materials, a groove is formed on a surface of the chuck to reduce a frictional area between the chuck and the substrate, thereby reducing the electrostatic field between the chuck and the substrate.
FIG. 2 illustrates a cross sectional view of the chuck surface according to the related art. As shown in FIG. 2, a chuck 51 used during an exposing process is provided with a substrate loading unit 53 for loading a substrate 50 and a lift bar mounting unit 55. A lift bar 57 is mounted in the lift bar mounting unit 55 before the substrate 50 is loaded on the substrate loading unit 53, and is used to prevent bending of the substrate 50. When using the lift bar 57, the chuck 51 has to be provided with the lift bar mounting unit 55. The substrate 50 transferred by the lift bar 57 is loaded to the substrate loading unit 53 as the lift bar 57 moves in the lift bar mounting unit 55.
The substrate 50 loaded on the chuck 51 is exposed to light irradiated from the upper side. If the layer on the substrate 50, which will be etched, is formed of a transparent material (for example, an ITO layer for forming pixel and common electrodes), light passes through the substrate 50 and is reflected by the chuck 51. Since the light passes through the substrate 50 again, the light passes through the photoresist twice.
When the pixel electrode or the common electrode of the in-plane switching LCD device is formed of a transparent electrode, a width of the electrode determines the aperture ratio. While forming the pixel electrode and the common electrode in the exposing process, if the pixel and common electrodes have different exposure degrees from an instant region to another region on the substrate due to reflected light by the chuck, the width of the pixel and common electrodes become different in accordance with an intensity of the reflected light. Eventually, the width of the pixel and common electrodes is varied along the surface of the lift bar having non-uniform reflected light, thereby causing stains on a display.